1. Field of the Invention
The present invention relates generally to surgical instruments, and more particularly to a patellar milling clamp and adjustable stops used with patellar milling clamps.
2. Description of the Related Art
A patellar implant is applied to a prepared patella either by surface attachment, referred to as an onlay procedure, or by recessing the implant into the patella, referred to as an insetting procedure. In an onlay procedure, the posterior patella surface is milled flat, to provide a suitable surface for attachment of the implant. In an insetting procedure, the posterior patella surface is milled to provide a cavity for receiving the implant, with a rim of bone remaining around the periphery of the implant. In either procedure, the patella must be secured firmly, relative to the milling tools used, and the milling tools must be guided accurately against the patella as the milling procedure progresses.
Various types of clamps and holders have been used for securing a patella when performing milling procedures. It is known to provide tool guides associated with the clamps, so that the tool is guided accurately towards the patella. A clamp must be capable of securing patellae of different sizes, and the tool guide must be adaptable for use with different size graters required for different size implants.
It is desirable to provide a milling tool guide including a stop, so that continued advancement of the milling tool, and continued milling of the patella is prevented after a predetermined amount of surface milling has occurred. Tool stops generally are known, and have included apparatus to prevent further advancement of the milling tool dependent upon the amount of material remaining in the patella. For example, U.S. Pat. No. 5,129,907 “PATELLAR CLAMP AND REAMER WITH ADJUSTABLE STOP” includes an adjustable stop calibrated with indicia for indicating the thickness of patellar bone remaining when the stop is engaged. In using such a device, the surgeon is required to calculate the amount of patellar bone material to be recessed to accept a patellar implant in an insetting procedure. The surgeon must also consider and calculate the amount such that sufficient patellar bone thickness remains after resection. With stops of this type, more bone thickness than necessary may be removed for insetting the implant or for preparing and smoothing the surface to receive an implant in an onlay procedure.
What is needed in the art is a patellar milling clamp that securely holds a patella while guiding a tool against the patella during a milling procedure, with an adjustable stop adjusted to remove only a sufficient amount of bone for the implant being used, regardless of the original patella bone thickness.